Mercy
by Graceybrook
Summary: Cat succumbs to the black mercy and Kara has to save her


**This is my first SuperCat fic so please be kind :) This started as a little drabble and escalated a bit but this is for Meli!**

 **Prompt: Cat succumbs to the black mercy and Kara has to save her**

Kara felt weak as her phone slipped out of her hand, Alex's voice fading as the phone hit the floor. As impossible as it sounded Cat Grant had succumbed to the black mercy. Kara didn't know how and right now she didn't care; she only knew that she had to save her.

Cat woke to the smell of coffee brewing, confused Cat blinked wearily. When did she buy a coffee machine? Suddenly Cat sat up and gasped, who was brewing the coffee? Cat looked around her for something to use as a weapon. Picking up a vase she moved towards the kitchen, slowly, bracing herself as she rounded the corner poised to face her attacker.

"Kara?" Cat lowered the vase, somehow even more confused than she had been mere moments before.

"Good morning, I made you coffee, just the way you like it of course." Kara walked towards Cat with a mug in her hands, and moved kiss her on the cheek, stopping when she noticed Cat's demeanor. "Is everything okay? You look very confused."

Cat thought for a moment, trying to place what felt so strange before shrugging the sensation off and smiling up at Kara. "Everything's fine."

"Where is she?" Kara stormed into the DEO headquarters, all but running towards her sister who led her down a corridor to a closed off room, Cat Grant lying on the table inside, the black mercy clinging to her chest. "Where did you find her?"

"She was found in her apartment, an empty box lying next to her, we think it had the black mercy inside. We don't know who sent it." Alex's voice was soothing as she tried to calm Kara down.

"I have to help her, please Alex I need to save her."

Cat watched as Kara busied herself making breakfast. "You're staring again." Kara sounded amused as she looked up from the chopping board, her bottom lip caught between her teeth. "I'm sorry, I'm still getting used to this, to us."

Cat still felt confused, but the confusion was ebbing the more Cat looked at Kara. Kara placed her hand on Cat's and smiled warmly, "you and me both."

"I just feel like something's off though."

"I wouldn't worry about it, if it's important you'll remember." Kara kissed Cat on the cheek before turning back to breakfast.

"Okay Kara we're good to go, just remember that you can't force Cat to give up whatever fantasy the black mercy has created, she has to choose to give it up herself." Alex said as she fiddled with a few dials before turning back to Kara.

"I know, Alex you can't pull me out, I have to get her out first. Promise me."

Alex sighed, "I promise, please be careful, she'll get defensive and I don't want you getting hurt."

"Alex I'm practically indestructible on this planet-"

"That is not what I meant and you know it." Kara nodded slowly and smiled softly ay Alex who returned the smile and pulled the lever that sent Kara to join Cat's mercy.

Cat finished eating her French toast and sighed contentedly. "Kara I-" Cat's thought was cut short as a knock at the door interrupted her. Cat shrugged and got up to open the door, revealing Supergirl stood in the frame.

"Ms Grant thank god I found you. I need to talk to you…" Supergirl trailed off as she caught sight of Kara sat at the kitchen island.

"Supergirl what's wrong?"

"I uh what am I- what's Kara doing here?"

"She lives here, what are you doing here? Is someone in danger?" Cat asked, almost as confused as Supergirl.

"It's you. You're in danger, and I'm here to save you."

"Cat don't listen to her, she's lying. You're not in any danger here, why would you be? She's clearly gone mad with all the stress of being Supergirl!" Kara's voice was defensive as she walked to Cat's side and took her hand. "I won't let anything happen to you, I promise!"

Cat's brow furrowed as she thought through what Supergirl and Kara had said. "Supergirl if this is some sort of breakdown I can help you but I'm in no danger, you know where the door is."

"Ms Grant please you have to listen to me I'm trying to save your life!" Supergirl was getting desperate now.

"I'm going to call security." Kara said walking away from Cat.

Cat sighed, "Oh security won't be able to do anything Kara."

As Kara turned away Supergirl could see a hint of a smile "Ms Grant look, Kara is smiling, why would she be smiling unless this isn't really her, she knows how much Supergirl means to you, please you have to believe me."

"Oh Supergirl enough! You really have lost it, please leave." Cat almost spat the words at Supergirl as she turned to walk away.

"No please I can't lose you too! If you stay here I can't save you, this isn't real! I- Kara isn't real, she's a figment of your imagination, she's just a fantasy." Cat turned back to face Supergirl, her face falling slightly.

"Cat no of course I'm real, why wouldn't I be? Doesn't this feel real to you?" Kara all but ran over to join Cat again. "She's clearly jealous."

Cat was bewildered, trying to absorb everything at once, she didn't know who to believe. "Both of you be quite I need some time to think." Cat walked over to the couch and sat down, taking of her glasses she put her head in her hands.

"Supergirl, what exactly am I in danger from?"

"There's this species called the black mercy, it latches onto you and uses your deepest fantasy to trap you in your own mind, while it… while it drains your life away. It will leave you a vegetable. I can't reject the fantasy for you, you have to do it yourself, otherwise I can't save you." Supergirl walked over to where Cat was sat and bent down so Cats' face was level with her own.

"And if I do give up this fantasy…" Cat looked over at Kara, still stood by the door "I lose Kara?"

"So don't give it up. This is utter madness Cat. You aren't in any danger! Please Cat, if you give this up what happens to me?"

"She's not real Ms Grant. Nothing will happen to her." Supergirl pleaded "Please! I don't know how much longer I can stay here, how much longer _you_ can stay. I have lost so many people in my life and I don't want to lose you too! I need you, the world needs you, the real Kara needs you."

"Oh Supergirl how do you know what Kara wants? If I reject this 'fantasy' as you put it, I could lose her forever."

Supergirl bit her lip, itching to tell Cat the truth, that she could never lose Kara because she _was_ Kara.

"I can't! if this is just a fantasy, how do I know if the real Kara loves me like this one, is it really better to save me if I lose the love I have here?"

Kara was smirking now, she could see that she'd won this battle as she sat down next to Cat.

"I know Kara loves you, she does."

"How could you possibly know that? You barely know her! You met her once!" There was despair in Cat's voice edged with hope.

"But I do know, I do know… Ms Grant when I'm not Supergirl… I'm Kara!"

Cat sat up straight, her eyes going wide, turning her head to look at Supergirl, then Kara and back to Supergirl. "Kara take off your glasses."

"Why?"

"Just take them off, please." Cat's voice was shaking as Kara removed her glasses making Cat gasp. Cat looked back at Supergirl, whose lip was caught between her teeth as Cat stood back up, pulling Supergirl with her. "Prove it. Tell me something only Kara would know."

"The first thing you do when you get into the office and sit behind your desk is take your heels off, you'll have any salad as long as there's a cheeseburger on top, whole milk hasn't touched your lips in years."

"Supergirl can see through walls and has super hearing! That proves nothing!" Kara stood up angrily, desperately trying to hold onto Cat.

"She's right Supergirl, I just don't believe you. Please leave." Cat turned away from Supergirl into Kara's welcoming arms.

Supergirl let a single tear escape as she started to walk away from the embracing couple.

Something still felt off to Cat as she stood wrapped up in Kara's arms, arms that somehow felt familiar. "Wait." Cat left the safety of Kara's arms and followed Supergirl to where she had stopped by the door. Cat pulled Supergirl into a hug and realisation hit her. It was true. Kara was Supergirl. Suddenly Cat felt herself going faint as her whole world crashed around her.

Kara woke unexpectedly, sitting up she threw off the virtual reality helmet that helped her enter Cat's fantasy and looked worriedly between her sister and Cat. "What did you do? I told you not to pull me out! I was so close!"

Alex was about to respond before she was interrupted. "She didn't."

Kara turned to see Cat sitting up, the black mercy crawling away across the floor. Cat smiled warmly as Kara threw herself into her open arms, sobbing softly. "I thought I'd lost you."

"Never. What would I do without my Supergirl? My Kara."

 **Please review :)**


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